Peter Ford said the Whitehall department led by Boris Johnson and his predecessor Philip Hammond had “gotten Syria wrong every step of the way.” Ford, who was Britain’s ambassador to Syria from 1999 to 2003, said Britain had misread the situation in the country since the start of the conflict.

He claimed the UK’s tough talk followed by little action to back the rebels in Syria had preceded a rebellion that had “only led to hundreds of thousands of civilians being maimed and killed.”

“We have made the situation worse,” he added.

“It was eminently foreseeable to anyone who was not intoxicated with wishful thinking.”

Speaking to the Independent, he said the government had falsely claimed Syrian President Bashar Assad could not control the country, when he was now on his way to doing just that.

“They told us at the beginning that Assad’s demise was imminent. They told us he’d be gone by Christmas. They didn’t say which Christmas, so they could still be proven correct.

“But then they told us that the opposition was dominated by these so-called moderates. That proved not to be the case and now they’re telling us another big lie - that Assad can’t control the rest of the country. Well I’ve got news for them - he’s well on the way to doing so.”

Ford says when the conflict started, the UK should have either “put everything including our own forces onto the battlefield, or if our judgment, as it would have been my judgment, that was not realistic, refrain from encouraging the opposition to mount a doomed campaign.”

The Syrian Army has reported that it has taken full control of Aleppo after weeks of heavy bombing and fighting around the city.

The International Committee of the Red Cross said “all civilians who wished to be evacuated have been, as well as the wounded and fighters.”

After a meeting in Paris earlier this month, Johnson said there could be no military solution to the Syrian war, while the UK has consistently taken the line that Assad cannot be part of Syria’s future.